Question: $ { {-5} \times \left[\begin{array}{r}{-1} \\ {4} \\ {2}\end{array}\right] = {?} } $
Answer: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{r}{-5}\times{-1} \\ {-5}\times{4} \\ {-5}\times{2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{5} \\ {-20} \\ {-10}\end{array}\right]}$